[Quoth]

No, the Nxtpaper40 phone is much better than many phones. But no use for PDFs. Fine in sunlight.

NxtPaper 14 uses more advanced Nxtpaper 3.0 and is 14.25″ 3:2 aspect. Best device ever for PDFs. Cheaper than 10" approx eink and better display than eink with front light on. Only the 6″ to 8″ mono eink when frontlight is off in good ambient is better. Perhaps also the Scribe with front light off, but I don't have it to compare.

I've had two models of 10.3″ eink and various 4.7" to 8" eink models.

For reading reflowable ebooks the PaperWhite 3 isn't bad or Oasis 2 (have/had both), but Kobo 7" mono and 8" mono are best.

Pocketbook is good for epub and PDF on android. Nebo to import/export PDF and annotate on Android, far superior to eink based Nebo on Kobo.

I have the TCL Nxtpaper 40 (phone nxtpaper 2.0), TCL Nxtpaper 11 (nxtpaper 2.0 and approx 16:10 aspect, good for notes) and Nxtpaper 14 (3:2 aspect 14.25″ and Nexpaper 3.0). Some are LCD and some OLED.

The Nxtpaper 10 is older and may only be Nxtpaper 1.0 and isn't very bright. Only read reviews.

The Nxtpaper 50 seems less reliable for Mobile than Nxtpaper 40 in reviews, but both only good for real reflowable ebooks, music, audio books and my Nxtpaper 40 works fine as a phone.

The Nxtpaper 14 is also only tablet I ever had totally decent for webpages. The Pro isn't worth the extra money as it's features are only needed for gaming.

Nxtpaper 11 is better than eink 10.3″ Elipsa and reMarkable for PDFs, but nothing like as good as the Nxtpaper 14 for PDFs.

The Nxtpaper 11 takes micro SD card. The Nxtpaper 14 doesn't but has 256 G flash

The Nxtpaper 40 (phone, no use for PDFs) has 3.5mm jack & BT, microSD and dual SIM. So ideal pocket solution for all regular phone/android/music/real ebook/audio book.

You can get a Nxtpaper 40 AND Nxtpaper 14 for less than price of an iPhone or high ende larger eink.

But for reading novels at home you can't beat an 8″ Kobo Sage.

All three of my Nxtpaper models are fine in direct sunlight. Auto light outdoors and 14% to 19% manual indoors. Set sRGB and adjust theme and colour balance. The default theme tints bright grey and white!

Edit:
And the booby prize for most useless PDF reader sold as a PDF reader goes to 9.7″ Kindle DX and DXG. I have the DXG. A 6" PW3 is far better!